The mx350 like every other RF universal remote is IR only controlling remote, but uses its own RF frequency to do it from afar.

The only way the mx350 will communicate with the H20 is via IR, so you have to switch the H20 to IR, turning off the native RF on the H20.

If don't know how to switch the H20 back to IR tell me and I'll explain.

Your mx350 never controlled your H20 receiver directly via RF, it sent RF signals to its RF basestation, which in turn sent IR signals to the H20. Now that the H20 set to RF doesn't accept IR commands, your mx350 isn't working, turning the RF off on the H20 with restore the communiaction between the two.